Microsoft Security Bulletin MS16-077 - Important

10/11/20179 minutes to readContributors

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Security Update for WPAD (3165191)

Published: June 14, 2016 | Updated: August 9, 2016

Version: 1.3

Executive Summary

This security update resolves vulnerabilities in Microsoft Windows. The most severe of the vulnerabilities could allow elevation of privilege if the Web Proxy Auto Discovery (WPAD) protocol falls back to a vulnerable proxy discovery process on a target system.

This security update is rated Important for all supported releases of Microsoft Windows. For more information, see the Affected Software and Vulnerability Severity Ratings section.

The update addresses the vulnerabilities by correcting how Windows handles proxy discovery, and WPAD automatic proxy detection in Windows. For more information about the vulnerabilities, see the Vulnerability Information section.

Affected Software and Vulnerability Severity Ratings

The following software versions or editions are affected. Versions or editions that are not listed are either past their support life cycle or are not affected. To determine the support life cycle for your software version or edition, see Microsoft Support Lifecycle.

The severity ratings indicated for each affected software assume the potential maximum impact of the vulnerability. For information regarding the likelihood, within 30 days of this security bulletin’s release, of the exploitability of the vulnerability in relation to its severity rating and security impact, please see the Exploitability Index in the June bulletin summary.

[2]Windows 10 updates are cumulative. The monthly security release includes all security fixes for vulnerabilities that affect Windows 10, in addition to non-security updates. The updates are available via the Microsoft Update Catalog.

Note Windows Server 2016 Technical Preview 5 is affected. Customers running this operating system are encouraged to apply the update, which is available via Windows Update.

*The Updates Replaced column shows only the latest update in any chain of superseded updates. For a comprehensive list of updates replaced, go to the Microsoft Update Catalog, search for the update KB number, and then view update details (updates replaced information is provided on the Package Details tab).

Update FAQ

Are there any further steps I need to carry out to be protected from CVE-2016-3213 described in this bulletin?
Yes. It is important to note that the security update described in this bulletin for CVE-2016-3213 does not fully protect your system. You must also install the cumulative update 3160005 in MS16-063 to be fully protected from this vulnerability.

Are there any behavior changes that I should be aware of after installing this update?
Yes. This update changes the behavior of Auto Proxy Detection and NetBIOS, which may affect various scenarios, such as SMB, WPAD-based proxy detection, and so on. For more information, see Microsoft Knowledge Base Article 3165191.

Vulnerability Information

Windows WPAD Elevation of Privilege Vulnerability - CVE-2016-3213

An elevation of privilege vulnerability exists in Microsoft Windows when the Web Proxy Auto Discovery (WPAD) protocol falls back to a vulnerable proxy discovery process. An attacker who successfully exploited this vulnerability could bypass security and gain elevated privileges on a targeted system.

To exploit the vulnerability, an attacker could respond to NetBIOS name requests for WPAD. The update addresses the vulnerability by correcting how Windows handles proxy discovery.

The following table contains links to the standard entry for each vulnerability in the Common Vulnerabilities and Exposures list:

Workarounds

Click the Local Area Connection to be statically configured, and then from the File menu, click Properties.

In the list of components, click Internet Protocol (TCP/IP), and then click Properties.

Click Advanced, click the WINS tab, and then click Disable NetBIOS over TCP/IP.

Optionally, you can select the Use NetBIOS setting on the DHCP server if you are using a DHCP server that can selectively enable and disable NetBIOS configuration through DHCP option types.

Stop WPAD using a host file entry

Open the host file located at following location as an administrator: %systemdrive%\Windows\System32\Drivers\etc\hosts

Create the following entry for WPAD in the host file: 255.255.255.255 wpad.

**Impact of workaround.** Autoproxy discovery will not work, and for this reason, some applications, such as Internet Explorer, will not be able to load websites properly.
**How to undo the workaround. **
1. Open the host file located at following location as an administrator: **%systemdrive%\\Windows\\System32\\Drivers\\etc\\hosts**
2. Remove the following entry for WPAD in the host file: **255.255.255.255 wpad.**

An elevation of privilege vulnerability exists when Microsoft Windows improperly handles certain proxy discovery scenarios using the Web Proxy Auto Discovery (WPAD) protocol method. An attacker who successfully exploited the vulnerability could potentially access and control network traffic for which the attacker does not have sufficient privileges. The update addresses the vulnerability by correcting WPAD automatic proxy detection in Windows.

The following table contains links to the standard entry for each vulnerability in the Common Vulnerabilities and Exposures list:

Mitigating Factors

Workarounds

Open the host file located at following location as an administrator: %systemdrive%\Windows\System32\Drivers\etc\hosts

Create the following entry for WPAD in the host file: 255.255.255.255 wpad.

**Impact of workaround.** Autoproxy discovery will not work, and for this reason, some applications, such as Internet Explorer, will not be able to load websites properly.
**How to undo the workaround. **
1. Open the host file located at following location as an administrator: **%systemdrive%\\Windows\\System32\\Drivers\\etc\\hosts**
2. Remove the following entry for WPAD in the host file: **255.255.255.255 wpad.**

NetBIOS Spoofing Vulnerability - CVE-2016-3299

A spoofing vulnerability that could allow elevated privileges exists in Microsoft Windows when NetBIOS improperly handles responses. An attacker who successfully exploited the vulnerability could use it to hijack network traffic or render untrusted content in a browser outside of Enhanced Protected Mode (EPM) or an application container.

To exploit the vulnerability, an attacker whose system is joined to a local network could trick a user into believing that the attacker's system is a trusted network device. The update addresses the vulnerability by updating how NetBIOS validates responses.

Security Update Deployment

Acknowledgments

Microsoft recognizes the efforts of those in the security community who help us protect customers through coordinated vulnerability disclosure. See Acknowledgments for more information.

Disclaimer

The information provided in the Microsoft Knowledge Base is provided "as is" without warranty of any kind. Microsoft disclaims all warranties, either express or implied, including the warranties of merchantability and fitness for a particular purpose. In no event shall Microsoft Corporation or its suppliers be liable for any damages whatsoever including direct, indirect, incidental, consequential, loss of business profits or special damages, even if Microsoft Corporation or its suppliers have been advised of the possibility of such damages. Some states do not allow the exclusion or limitation of liability for consequential or incidental damages so the foregoing limitation may not apply.

Revisions

V1.0 (June 14, 2016): Bulletin published.

V1.1 (June 22, 2016): Bulletin revised to add an Update FAQ on behavior changes to be aware of after installing this update. This is an informational change only.

V1.2 (July 13, 2016): Bulletin revised to correct the workarounds for CVE-2016-3213 and CVE-2016-3236. This is an informational change only. Customers who have successfully installed the updates do not need to take any further action.

V1.3 (August 09, 2016): Bulletin revised to include an additional vulnerability, CVE-2016-3299. This is an informational change only. Customers who have successfully installed the updates do not need to take any further action.